1. Field of the Invention
This invention generally relates to a method of processing a signal having both a relatively high frequency fluctuation and a relatively low frequency fluctuation, such a voice signal, to extract the relatively high frequency fluctuation and more particularly to a novel method of extracting phonemic information and a linear phase filter particularly suited for use in such a method.
2. Description of the Prior Art
Signal A shown in FIG. 1 is a frequency distribution curve for one frame of voice signal, and, as shown, the curve A has a relatively slowly changing tendency, in which its output level decreases as the frequency increases, and also a relatively quickly changing tendency which is indicated by three local peaks B.sub.1, B.sub.2 and B.sub.3, constituting phonemic information. In one method of recognition of vocal sound, the phonemic information B.sub.1, B.sub.2 and B.sub.3 is extracted from the voice signal A to be used in the recognition of vocal sound. In this case, however, when extracting phonemic information from a voice signal, typically, there arises a problem of a deterioration of high frequency components depending on the sound producing characteristic of the sound source.
In order to carry out the extraction of phonemic information while maintaining high accuracy up to higher frequencies, it has been proposed to carry out correction using an approximate straight line obtained by the least square method. According to this proposed method, the voice spectral distribution X.sub.i, where i=channel number, is approximated by a straight line defined by y=ai+b, whereby X.sub.i -(ai+b) is defined as a new characteristic parameter of the new voice spectral distribution. In this case, a and b are determined by ##EQU1## However, the calculation for and b is rather complicated, time-consuming and expensive.